1. Field of the Invention
The present invention relates in general to an ocular diagnostic tool and, more particularly, to an colorimetric pupil light reflex testing device for diagnostic assessment of the ocular and central nervous system diseases based on melanopsin and non-melanopsin spectral light properties.
2. Description of the Prior Art
It is known in the art to diagnose various types of abnormalities in humans and animals using the reaction of a pupil to specific wavelengths of light. The pupil light reflex evaluation provides an objective method for assessing function of the retina and optic nerve. The pupil light reflex is driven by photoreceptor activity (rods and cones) and a subpopulation of retinal ganglion cells, which contain a photosensitive pigment called melanopsin. Physiological spectral properties of healthy retinas provide a baseline against which to use a calorimetric device for testing the pupil for both photoreceptor-mediated pupil light reflex and melanopsin-mediated pupil light reflex.
Melanopsin is a photosensitive pigment activated by a high light intensity (30 kcd/m2 or higher) with a peak spectral sensitivity in the blue (480+/−50 nm) range. Photoreceptor-mediated pupil light response is activated by different wave lengths, but the activation occurs at very low light intensities (25 cd/m2). Since red light (630 nm+/−40 nm) can activate photoreceptor-mediated pathways, the melanopsin mediated pupil light response can not be activated since spectral properties of the red light fall behind the melanopsin spectral sensitivity.
Diagnosis of ocular abnormalities based upon pupil-light reflex is known in the art. A pupil of an animal or human is exposed to a specified wavelength of blue light and then to a specified wavelength of red light. A veterinarian or doctor can then make various diagnoses based upon pupil-light reflex to exposure to the two wavelengths. However, in the past, making an ocular abnormality diagnosis based upon pupil-light reflex has been limited by the use of white light only for evaluation of the pupil light reflex which contains both red and blue wavelengths of light.
To obtain the required wavelengths of blue and red light, prior art systems combined white light with different color filters. The filters block out all of the light at undesired wavelengths, but will let pass the desired wavelength for which the filter was designed. The width of the pass band of wavelengths can be wide or narrow, based upon the filter type. In addition, prior art filters often “leak” light at undesired wavelengths, which can lead to an ambiguous or even incorrect diagnosis. Although there are filters which minimize leakage, such filters are typically quite expensive and hard to find in usable sizes. The efficiency of prior art filters is typically low. Prior art filters need to have a very narrow wavelength band pass (approx 3 nm), centered around 480 nm for blue light and around 630 nm for red light. This means that only about 1-3% of total light is passing through the filter.
An extremely powerful white light is necessary in order to have a decent light output after the filter. Such lights consume a significant amount of power, generate intense heat, are expensive and require expensive systems to operate effectively. Also, in time, the incandescent bulbs have a decrease in light output and need to be replaced after a specific hours of usage. Incandescent lamps dim as they age (projector lamps for example are rated for approximate 2000 hours and they cost $300-$600 or more to replace.) A filter with a wider wavelength band pass can be used in order to achieve a better transmittance and increase the efficiency, but at the cost of diagnostic precision. Additionally, given the large amount of light required and the reduction of light transmission associated with prior art filters, it is often necessary to provide an instrument to measure the light output in order to determine the precise luminance of the light irradiating the pupil (candela/square meter). Luminance is a photometric measure of the density of luminous intensity in a given direction. It describes the amount of light that passes through, or is emitted from, a particular area, and falls within a given solid angle. The luminance indicates how much luminous power will be perceived by an eye looking at the surface from a particular angle of view. Luminance is thus an indicator of how bright the surface will appear. In this case, the solid angle of interest is the solid angle subtended by the eye's pupil. Instruments capable of accurately measuring such luminous are often expensive and difficult to use.
The requirement of a large intensity light source, a specific wavelength filter and a luminance measuring instrument leads to a prior art process requiring a large amount of heavy, complicated and expensive instruments. It would be desirable, therefore, to provide a system for reducing the weight, cost, complexity and variability associated with such prior art systems.
Additionally, as such prior art systems typically require hot lights, filters and luminescence meters to be held at various times and at various locations, it is often difficult to conduct a diagnosis with a single individual. Even if a single individual could accomplish the diagnosis, the prior art process typically does not allow the user a free hand to manipulate the eyelid and/or a camera to record the results. It would, therefore, be desirable to provide a system which could be used by a single operator with a single hand.
Utilization of a filter in front of a light source typically leads to a certain amount of variability in the light source being transmitted. Even with a luminescence meter recording the light passing through the filter, the leakage of the filter combined with the movement of the filter by the user can lead to an indeterminate result. Therefore, it would be desirable to provide a method for diagnosing ocular abnormalities using pupil-light reflex, which is accurate and consistent.
Yet another drawback associated with the prior art is that given the variability and intensity of prior art machines, prior art machines sometimes require the user to increase the intensity beyond a desirable level to elicit the response necessary for the diagnosis. Increasing the light intensity beyond the desired diagnostic level, however, can lead to additional damage of the eye. Conversely, in situations where the power is decreased to avoid damage to the eye, the diagnosis often cannot be made, or the light is left on the pupil for an extended period of time in an effort to elicit the response, thereby again leading to the potential for damage to the eye associated with overexposure. It would, therefore, be desirable to provide a light source with a consistent output to decrease the likelihood of damage to the eye associated with the diagnosis.